1. Technical Field
The present invention relates to a cleaning method and a cleaning apparatus for cleaning a glass substrate with a color filter. More particularly, the present invention relates to a cleaning method and a cleaning apparatus for cleaning a glass substrate with a color filter including a pattern of transparent electrode, which is made of ITO (indium tin oxide: an alloy of indium oxide and tin oxide) or IZO (an alloy of indium oxide and zinc oxide), or the like, and which is formed on a pigment pattern. Yet more particularly, the present invention relates to a cleaning method and a cleaning apparatus for cleaning a glass substrate with a color filter, which can remove an organic contaminant on the ITO or IZO film by exposure to ultraviolet radiation.
2. Prior Art
A portable personal computer (PC) called as a laptop type or a notebook type has been developed, fabricated and widely used with the recent advance of technology. Generally, these portable computers use various display devices utilizing liquid crystal, electroluminescent (EL), plasma, etc. for the reason that these display devices are thin, light weight and low power consumption and does not prevent the portability of the computer.
This type of display device includes glass substrates on which the electrodes are formed as a major component. For example, the liquid crystal display device includes two glass substrates and a liquid crystal material filled in a space between the two substrates. The pattern of the electrodes is formed on a surface of the substrate which faces the liquid crystal material to apply an electric field to the liquid crystal material. In the case of the color liquid crystal display device, a color filter is formed on the upper glass substrate of the two glass substrates. In this case, the transparent electrodes are formed to cover the surfaces of pigment portions for displaying a red (R) color, a green (G) color and a blue (B) color. An alloy, such as ITO (indium tin oxide: an alloy of indium oxide and tin oxide) or IZO (an alloy of indium oxide and zinc oxide), is generally used as the transparent electrode. For example, the transparent electrode of the ITO film is formed by depositing In-Sn metal on the glass substrate and annealing them to oxidize them.
FIG. 8 shows a cross section of the glass substrate and the color filter. As shown in the FIG. 8, a film of a black matrix (BM) and the pigment portion are formed on the glass substrate in this order. The glass substrate is made of alkali-free borosilicate glass or quartz glass of the thickness of 0.7 mm. The pigment portion has the one of the colors R, G and B, and its upper surface is covered by the transparent electrode, such as the ITO film, of the thickness of 1500.+-.200 .ANG.. The BM layer, such as a Cr layer, is formed underside of the color filter layer to shut off the radiation illuminated on a portion other than an effective portion of a picture element for emphasizing the black to improve the contrast ratio, as well known in the art.
Undesired organic material, such as dye, tends to adhere or stick on the glass substrate. If the organic contaminant adheres on the glass substrate, undesired problems, such as a change in quality of the liquid crystal sandwiched between the glass substrates, a generation of defects in the displayed image may be occurred. To prevent these problems, it is necessary to keep the glass substrates having the transparent electrodes, such as the ITO film, the IZO film, formed thereon in a clean condition in the fabrication process.
It has been broadly known in the art that a cleaning using the ultraviolet radiation is effective to remove the organic material. The cleaning process is performed by a mechanism that activated oxygen is generated by a photochemistry action of the ultraviolet radiation, i.e. the exposing to the ultraviolet radiation, and the organic material is oxidized by the action of the activated oxygen and changes to volatile molecules.
In the case of the cleaning of the organic material by exposing to the ultraviolet radiation, however, the necessary organic material, which should not be removed, on the substrate is quite capable of being damaged along with the unnecessary organic material since the entire surface of the glass substrate is exposed to the ultraviolet radiation.
Only the cleaning apparatus for cleaning the glass substrate which uses a low pressurized mercury lamp having an output wavelength of 254 nm has been widely used in the fabrication lines. The ultraviolet radiation having the relatively long wavelength of 254 nm can transmit through the transparent electrode layer, such as the ITO film, the IZO film etc. The ultraviolet radiation transmitting through the transparent electrode layer exerts a bad influence, such as a discoloring on the pigment portions to degrade the function of the color filter along with the removal of the unnecessary organic material. To solve this problem, the exposing time is shortened in the cleaning using the ultraviolet radiation. However, the shortening of the exposing time ills arises a new problem of insufficient cleaning. An easygoing way of thinking is possible which uses the ITO film or the IZO film of a large thickness to protect the pigment pattern from being exposed to the ultraviolet radiation. However, the thickness of the ITO film or the IZO film must be in the range of 1300 .ANG..about.1700 .ANG. due to the requirement to raise the transmittance of the ITO film or the IZO film.
One of the object of the present invention is to provide an excellent cleaning method and a cleaning apparatus for cleaning a glass substrate with a color filter.
Another object of the present invention is to provide an excellent cleaning method and a cleaning apparatus for cleaning a glass substrate with a color filter including a pattern of transparent electrode, made of ITO (indium tin oxide: an alloy of indium oxide and tin oxide) or IZO (an alloy of indium oxide and zinc oxide), etc., is formed on a pigment pattern.
Another object of the present invention is to provide an excellent cleaning method and a cleaning apparatus for cleaning a glass substrate with a color filter which can effectively remove the organic contaminant deposited on the ITO film or the IZO film by exposing to ultraviolet radiation.